The present invention relates to an igniter for an air bag system used in an air bag system using a bus system and a method for controlling operation of an air bag system using the same.
An air bag system for protecting a passenger from an impact at a time of collision of a vehicle is indispensable, and the air bag system needs to be reduced in weight from a demand for reducing weight of a whole vehicle. Recently, kinds and the total number of air bags such as an air bag for a driver side, an air bag for a passenger side next to the driver, an air bag for a rear seat side, and an air bag for an side impact are increasing, and therefore, a lighter air bag system is in greater demand.
In a current air bag system, an electronic control unit (ECU) connected to a power source (a battery in a vehicle) and an impact detecting sensor are individually connected to individual gas generators (a gas generator and an air bag are accommodated in a module case). An aspect of the connection between the ECU and the individual gas generators is shown in FIG. 13.
As shown in FIG. 13, the ECU and an igniter (FIG. 14) of each of the individual gas generators are necessarily connected to each other through two conductors, and thereby, conductors double the number of the total number of igniters are required. Having many conductors contributes largely to weight increase in an air bag system. In view of constraints at a time of assembling vehicle parts, the ECU and the individual gas generators are not connected by only the conductors but connected by connecting plural conductors via plural connectors, and thereby, there occurs a serious problem such as a weight increase due to use of the connectors and a cost increase due to increase of the number of the connectors. Further, increase in volume (weight) of the ECU due to increase in volume of a capacitor incorporated into the ECU as a backup power source for activating all the igniters (serving at a time of a disconnection between the power source and the ECU) is another serious problem.
In view of the above, a trial for reducing a conductor weight required for connection between the ECU and the individual gas generators by utilizing a bus system in the air bag system has been examined. An aspect of the air bag system utilizing this bus system is shown in FIG. 1.
As shown in FIG. 1, an air bag system is constituted by providing bus lines comprising plural loop wires passing through the ECU and connecting each of the individual gas generators to the bus line through two conductors (three or more conductors when occasion demands). In a case of such an air bag system as shown in FIG. 1, since only gas generators required corresponding to a collision situation of a vehicle are activated, an integrated circuit receiving information transmission from the ECU and a capacitor supplying a current for activating an igniter are provided in each of the individual gas generators. In the case of utilizing a bus system, the total number of capacitors is increased, but since the capacitors are distributed and arranged in the ECU and the respective igniters, the capacitance and weight of the capacitor per igniter is reduced. As a result, since the weight of the capacitors in this case is remarkably reduced as compared with the weight of the capacitors for backup in the air bag system shown in FIG. 13, a large weight reduction is achieved as the whole system in addition to largely reducing the amount of use of conductor, which is expected to be put in a practical use in the air bag system. Incidentally, there have been known JP2000-241098A, JP2000-513799A and Japanese Patent No. 2707250 as the prior art utilizing the bus system.
An object of the present invention is to provide an igniter for an air bag system which achieves a large weight reduction in an entire air bag system by introducing a bus system into the air bag system, and which can ensure reliability and rapidness of operation similar to those in a conventional art, and which can obtain a high reliability, and an operation control method of an air bag system utilizing the same.
An invention described in claim 1 provides, as one means for solving the above problem, an igniter, for an air bag system, which is one or at least two igniters incorporated in the plural of the gas generators and used in an air bag system comprising an electronic control unit connected to a power source and an impact detecting sensor, and plural module cases which are connected to the electronic control unit and accommodate plural gas generators and plural air bags, wherein,
in the air bag system, a bus line comprising plural loop wires which pass through the electronic control unit is provided to supply and transmit currents and required information, and individual gas generators accommodated in the plural module cases are connected operationally by plural conductors branched at predetermined portions from the bus line,
the one or at least two igniters incorporated in the gas generator is an electric igniter which is provided with a heat generating portion and a priming coming in contact with the heat generating portion, and the igniter and the bus line are connected to each other through plural conductors, and the capacitor and the integrated circuit recorded with information to exhibit required functions are provided in the igniter, and a current for igniting the priming is supplied to the one or at least two igniters through a capacitor inside the igniter.
The numbers of the loop wires forming the bus line and the conductors for connecting the bus line and the gas generators may be two, three, or four or more, respectively, but, in view of simplification of the entire system, two is preferable.
The priming is not limited to a specific one, but a combination of a metal or the like and an oxidizing agent such as perchlorate is preferable, a combination of a metal such as zirconium, titanium, and hafnium and perchlorate is more preferable, and a mixture (ZPP) of zirconium and potassium perchlorate is particularly preferable. Desirably, the ZPP is formed in particle shape and particle diameters of zirconium and potassium perchlorate are adjusted.
A capacitance of the capacitor is preferably not more than 24 xcexcF, more preferably not more than 12 xcexcF, further more preferably not more than 6 xcexcF.
Preferably, the air bag system using an igniter for an air bag system of the present invention is activated such that a current for igniting the priming in one or at least two igniters is supplied via the capacitor inside the igniter, and that a time period for supplying a current from the capacitor to the heat generating portion is the period from the point where a current value reaches the current value corresponding to 5% of the maximum current value to the point where it is reduced down to the current value corresponding to 5% of the maximum current value, which is within 500 xcexcsec. In this case, the maximum current value in the period for supplying a current is a current value sufficient to ignite the priming. The period for supplying a current is preferably within 200 xcexcsec, and more preferably within 100 xcexcsec. Incidentally, a current value at this time varies depending on a resistance value of the heat generating portion in the igniter, and it is determined on the basis of presence or absence of the waveform converting circuit, the constitution of the waveform converting circuit, a particle diameter of a priming, a shape of the heat generating portion and the like.
In the case of a conventional air bag system, since a current for activating an igniter flows from a power source (a battery) with a relatively large capacitance at 1.2 A for about 2 msec, that is, at a relatively low current for a relatively long time, a waveform of an ignition current (a vertical axis denotes a current value (A) and a horizontal axis denotes a time (xcexc sec)) becomes rectangular.
In the present invention, however, since an electric current for activating an igniter is supplied from a capacitor with a relatively small capacitance, it is preferable that a relatively high electric current flows for a short time, because ignition of the igniter is made smoother and ignition energy itself can be made smaller. The waveform of the ignition current at this time (a vertical axis denotes a current value (A) and a horizontal axis denotes a time (xcexcsec)) becomes a discharging waveform expressed by the following formula (I) when discharging starts at a time of time t=0:
i(t)=(V0/R)xc3x97exe2x88x92t/CRxe2x80x83xe2x80x83(I)
(In the formula, v0 represents a capacitor charging voltage (V), R represents a circuit resistance (xcexa9), C represents a capacitor capacitance (xcexcF), t represents a time (xcexcsec), and i represents a current (A)).
When such a discharging waveform expressed by the formula (I) is employed, a current value becomes larger than a conventional rectangular waveform, but a current conduction time is shortened. Therefore, the ignition energy itself is reduced largely.
In the present invention, when a period in which a stable current supplying is being maintained after reaching a desired current value is defined as t (xcexcsec) and a period from a start of waveform rising to stopping of current supplying for making the heat generating portion generate a heat is defined as T (xcexcsec), it is preferable that a relationship (t/T) between these t and T is in the range of 0xe2x89xa6t/T less than 0.2 or 0.5 less than t/T less than 1.
In the case of 0 less than t/T less than 0.2, a waveform of a current is similar to a discharging waveform (a waveform similar to a triangle) obtained when electricity stored in the capacitor is applied to the heat generating portion directly. In case of 0.5 less than t/T less than 1, a waveform of a current is similar to a waveform (a waveform similar to a triangle) obtained when a discharging waveform is converted through a discharging waveform converting circuit for converting a waveform of a current stored in a capacitor to a signal waveform of a current for igniting the priming or the like.
The above inventions is preferably provided with a capacitor and the integrated circuit having required functions, and further preferably, it is provided with a discharging waveform converting circuit. The discharging waveform converting circuit is one having a function for converting the discharging waveform expressed by the following formula (I) to a triangular waveform or a trapezoidal waveform. In addition, in order to provide a similar converting function, a coil can be interposed in a connecting circuit between the capacitor and the heat generating portion, and the discharging waveform converting circuit can further be provided in the integrated circuit in view of simplification of the entire system.
An invention described in claims 6 and 7 provides, as one means for solving the above problem, an igniter for an air bag system, which is one or at least two igniters incorporated in the plural of the gas generators and used in an air bag system comprising an electronic control unit connected to a power source and an impact detecting sensor, and plural module cases which are connected to the electronic control unit and accommodate plural gas generators and plural air bags, wherein,
in the air bag system, a bus line comprising plural loop wires which pass through the electronic control unit is provided to supply and transmit currents and required information, and individual gas generators accommodated in the plural module cases are connected operationally by plural conductors branched at predetermined portions from the bus line,
the one or at least two igniters incorporated in the gas generator is each electric igniter which is provided with a heat generating portion and a priming coming in contact with the heat generating portion, and the igniter and the bus line are connected to each other through plural conductors,
a capacitor, an integrated circuit in which information for developing a required function is stored, and the heat generating portion is provided on one substrate in each igniter, and the substrate is provided vertically, and
at least the capacitor and the integrated circuit on the substrate, and the priming are not in contact with one another, and a current for igniting a priming is supplied to the igniter through the capacitor in the igniter.
Further, the present invention provides, as one means for solving the above problem, an igniter for an air bag system, which is one or at least two igniters incorporated in the plural of the gas generators and used in an air bag system comprising an electronic control unit connected to a power source and an impact detecting sensor, and plural module cases which are connected to the electronic control unit and accommodate plural gas generators and plural air bags, wherein,
in the air bag system, a bus line comprising plural loop wires which pass through the electronic control unit is provided to supply and transmit currents and required information, and individual gas generators accommodated in the plural module cases are connected operationally by plural conductors branched at predetermined portions from the bus line,
the one or at least two igniters incorporated in the gas generator is each electric igniter which is provided with a heat generating portion and a priming coming in contact with the heat generating portion, and the igniter and the bus line are connected to each other through plural conductors,
each igniter has a capacitor and an integrated circuit in which information to exhibit a required function which are provided on the one substrate, and the substrate is provided vertically,
a header, which supports an electroconductive member for supplying and transmitting a current between the substrate and the heat generating portion, sections vertically between the substrate and the priming, and the substrate is arranged below the header and the heat generating portion is arranged above the header, and
a current for igniting the priming is supplied to one or at least two igniters through the capacitor in the igniter. In this case, as long as the heat generating portion is provided above the header, it may be provided on a header surface or it may be provided over the header, separated from the header surface.
In the above respective inventions, the numbers of the loop wires forming the bus line and the conductors for connecting the bus line and the gas generators may be two, three, or four or more, respectively, and two is preferable in view of simplifying the entire system.
In the above respective inventions, the priming is not limited to a specific one, but a combination of a metal or the like and an oxidizing agent such as perchlorate is preferable, a combination of a metal such as zirconium, titanium, and hafnium and perchlorate is more preferable, and a mixture (ZPP) of zirconium and potassium perchlorate is particularly preferable. Desirably, the ZPP is formed in particle shape and particle diameters of zirconium and potassium perchlorate are adjusted.
In the above respective inventions, a capacitance of the capacitor is preferably not more than 24 xcexcF, more preferably not more than 12 xcexcF, and further preferably not more than 6 xcexc.
In the above invention, the respective igniters of the respective gas generators are provided with a capacitor and an integrated circuit having a required function, and preferably, a discharging waveform converting circuit is further provided.
In the above invention, the integrated circuit (and the discharging waveform converting circuit, if required) is provided on one surface of the substrate and the capacitor (and the discharging waveform converting circuit, if required) is provided on the other surface. The heat generating portion may be provided on either surface, but desirably, it is provided on the same surface as the integrated circuit to facilitate circuit formation (a soldering work). Further, if the waveform converting circuit is provided, preferably, it is provided in the integrated circuit in view of simplifying the entire system.
In the above invention, such a structure can be employed that the substrate is fitted to penetrate a header for forming a priming holding space together with a cup member for holding the priming, and the capacitor and the integrated circuit are positioned below the header, and the heat generating portion projects above the header to come into contact with the priming.
When the heat generating portion is provided on the header, the following methods or the like can be employed: a method for welding a wire for heat generation on the header to fix the heat generating portion; a method for, after pasting a metal foil on an insulating substrate comprising an aluminum with oxidized coating, a glass, epoxy resin, phenol resin, polyimide or the like, forming the heat generating portion by etching; a method for forming the heat generating portion by performing vapor deposition of an electroconductive material on a pattern-masked insulating substrate; a method for printing electrical electroconductive material on an insulating substrate.
By providing the integrated circuit and the capacitor on different surfaces of the substrate in this manner, a compact structure can be achieved as compared with a case of providing on one surface. Further, by providing the priming above the header and providing the substrate below the header, the integrated circuit or the capacitor does not come in contact with the priming, so that pollution of the capacitor or the integrated circuit due to the priming can be prevented and, in addition thereto, a possibility of erroneous activation of the igniter can also be eliminated.
In the above invention, such a structure can be employed that the integrated circuit and the capacitor (and the discharging waveform converting circuit, if required) are provided on one surface of the substrate. The heat generating portion may be provided on either surface, but desirably, it is on the same surface as the integrated circuit and the capacitor. The discharging waveform converting circuit functions to convert the discharging waveform expressed by the formula (I) into a triangular waveform or a trapezoidal waveform.
In the above invention, such a structure can be employed that a portion of the substrate except for the heat generating portion is sealed with thermoplastic resin containing glass fibers, thermosetting resin such as epoxy resin, organic and inorganic insulating material such as glass, and the heat generating portion is in contact with the priming. When a substrate having such a structure is used, the substrate exists above the header for supporting pins which serve as interposing members to supply and transmit a current and required information to the integrated circuit and the capacitor.
In case of employing such a structure, the capacitor and the integrated circuit are protected and the capacitor and the integrated circuit do not come in contact with the priming, and thereby, pollution of the capacitor and the integrated circuit due to the priming can be prevented.
In the above invention, an electroconductive pattern is formed on a substrate by etching, including connecting portions which connect the integrated circuit with the heat generating portion, the capacitor and the bus line, and the heat generating portion of the igniter. At this time, the conductor pattern forming the connecting portions which connect the integrated circuit with the heat generating portion, the capacitor and the bus line can be two routes for each connecting portion, i.e., the total six routes as shown in FIG. 8 and FIG. 9. Incidentally, as the etching, wet etching, dry etching (plasma etching, sputter etching, reactive ion etching) photo etching or the like can be applied.
When such conductor patterns are used, the number of connecting portions obtained by soldering is reduced as compared with a case of connecting all of the integrated circuit, the heat generating portion and the capacitor with a conductor and soldering the connecting portions. As a result, a possibility of a malfunction in activation due to a resistance value and a loose connection is decreased, which is preferable. Furthermore, by providing such conductor patterns, a wiring is facilitated, and manufacturing is made easier as compared with a case of providing a bridge wire as the heat generating portion.
In the above first to third solving means, as the integrated circuit recorded with information to exhibit required functions, the one recorded with information for exhibiting one or at least two functions selected from the group of (i)a function for detecting abnormality of the heat generating portion of the igniter in the gas generator, (ii)a function for identifying each of the plural gas generators and (iii)a function for detecting a malfunction of the capacitor can be used. And additionally, it is preferable that (iv)a circuit for preventing the igniter from being activated erroneously due to a noise generated outside the igniter is provided in the igniter.
Usually the integrated circuit is provided with a basic function to activate a proper gas generator for protecting the passenger according to a situation of a vehicle collision upon receiving a signal from the ECU. In addition thereto, by providing the above various functions, quality check of a product at a time of shipping, workability at a time of assembling and safety at an actual use (while driving a vehicle) and the like can be improved properly.
(i) The Function for Detecting Abnormality of the Heat Generating Portion of the Igniter in the Gas Generator:
As one of conditions required for the gas generator to activate normally, a contacting state between the heat generating portion of the igniter and the priming has to be good (the heat generating portion and the priming has to be brought in press-contact with each other). For example, when there is a gap between the heat generating portion and the priming, it is considered that there occurs a malfunction such that the priming is not ignited when the igniter is actuated or an ignition is delayed. Further, when the heat generating portion is disconnected or have been half-disconnected, a similar malfunction occurs. For this reason, by recording information for detecting the malfunction in the integrated circuit, an inferior product can be removed at a time of shipping, and by detecting abnormality at a practical use (while driving a vehicle), a prompt exchange can be performed.
Detecting theory for abnormality of the heat generating portion (Thermal Transient Test; issued on pages 461 to 478 in xe2x80x9cProgress of International Pyrotechnic Semina xe2x80x9d on July 1980 by A. C. Munger) is as follows: when contacting state of a heat generating portion and a priming is good, most part of calorie generated by flowing of a constant current is conducted to the priming, so that the temperature of the heat generating portion does not rise so high. On the other hand, when the contacting state of the heat generating portion and the priming is bad, transfer of heat is less, so that the temperature rising of the heat generating portion becomes higher than a normal case. Therefore, a malfunction is detected by detecting a temperature change due to such a difference in contacting state as a resistance value change and utilizing a temperature coefficient of metal resistance [r=r0 (1+xcex94xcex1T)] to obtain the temperature of the heat generating portion. More specifically, after a resistance r is measured when a current i which is too weak to raise the temperature up to igniting the igniter, a resistance R is measured when a current I of 10 to 15 times of the current i is flowed (the temperature of the heat generating portion becomes about 50 to 100xc2x0 C., but the priming is not ignited with such a temperature), so that the resistance change due to the temperature change of the heat generating portion is obtained as a voltage change with comparisons of I and i and of R and r. Thus, such measurement information is recorded in the integrated circuit.
(ii) The Function for Identifying Each Plurality of Gas Generators:
For the gas generator for an air bag, various kinds of gas generators such as one for a driver side, one for a passenger side next to the driver, one for a side impact (for a side collision), one for a curtain air bag and the like have been practically used. For example, in the case of the gas generator for a side impact, the total four gas generators are mounted for a driver side, a passenger side next to the driver, two rear seat sides respectively. For this reason, though different information pieces are recorded in the respective integrated circuits of the gas generators for the driver side, for the passenger side next to the driver, and for two rear seat sides, when these information pieces are recorded at a time of assembling the igniters or the gas generators or before assembling, since the igniters or the gas generators have the same appearance, it is necessary to distinguish the gas generators having the same appearance and having different information pieces recorded or the igniters having the same appearance before assembling such that a wrong one is not taken to store and transport them, which becomes much complicated. Furthermore, with one for a driver side mounted to a vehicle erroneously as one for a passenger side next to the driver, when activation information of an air bag for a driver side is sent from the ECU, such an erroneous activation that an air bag for a passenger side next to the driver is inflated occurs eventually.
Therefore, by recording of information for developing identifying function for each plurality of gas generators after assembling of gas generators (when differences of gas generators can be recognized apparently), after gas generators are assembled in module cases (when differences of module cases can be recognized apparently) or after gas generators are mounted to a vehicle, storage, transportation, management and the like of gas generators can be made easy, so that a mistake or a confusion is prevented from occurring at a time of mounting of gas generators.
It is preferable that the information for developing an identifying function for each plurality of gas generators are recorded after assembling the gas generators, it is more preferable that the information pieces are recorded after the gas generators are assembled in the module cases, and it is further preferable that the information pieces are recorded after the module cases are mounted to a vehicle.
(iii) The Function for Detecting a Malfunction of the Capacitor:
The information for developing a function for detecting a malfunction of the capacitor also includes confirmation information of a mounted state (soldered state) of a capacitor to a substrate and the like in addition to information for measuring a pulse response or a dielectric dissipation factor.
After mounted to the vehicle, since the capacitor repeats charging and discharging, the capacitor deteriorates with age. However, abnormality is detected at a time of a practical use (while driving a vehicle) by recording information which can confirm a malfunction due to this deterioration in the integrated circuit in advance, so that a prompt exchange can be performed. Furthermore, by recording information for confirming the soldered state in advance, an inferior product can be removed at a time of shipping.
(iv) A circuit for preventing the igniter from being activated erroneously by a noise made outside the igniter (a noise countermeasure circuit).
For example, when a large current flows at a time of activating a cell motor in a vehicle, in case of not providing a noise preventing circuit, there is a possibility that a noise (a noise causing an uncomfortable unusual sound occurrence while listening to the radio) generated due to this current is transmitted from a vehicle body to flow in an igniter. Due to that the noise is transmitted in this manner, a possibility that an igniter causes an erroneous activation becomes high. Accordingly, by mounting a device constituted to prevent a current from flowing from a vehicle side to an igniter side, for example, a diode or a varistor (a non-linear resistance element) as the noise countermeasure circuit (a circuit for preventing an igniter from being activated erroneously), the above-described erroneous activation of the igniter can be prevented
The present invention according to claim 30 provides, as another solving means for the above problem, an igniter of an air bag system which is at least two igniters share one capacitor and one integrated circuit inputted with information to exhibit required functions when the air bag system of the above invention has at least two igniters for each of the plural gas generators.
The at least two igniters share one capacitor and one integrated circuit inputted with information for exhibiting required functions, and further, they share a discharging waveform converting circuit which is provided, if required, to convert a signal waveform of a current for igniting the priming stored in the capacitor for each igniter. And thereby, the entire system can further be reduced in weight. In this case, the discharging waveform converting circuit may be assembled into the integrated circuit.
The invention described in claim 31 provides, as another means for solving the problem, an igniter of an air bag system wherein each igniter has a capacitor and an integrated circuit inputted with information to exhibit required functions, and further has two pins for supplying and transmitting a current and required information to at least two igniters from the bus line when the air bag system of the above invention has at least two igniters for each of the plural gas generators.
In the igniter of the air bag system according to the above first to fifth solving means, there is provided with a circuit which, among the currents from the bus circuit for charging the capacitor and the required information, is a circuit, for charging the capacitor, having a function for rectifying a current to flow into a capacitor to be charged (hereinafter, referred to as xe2x80x9ca rectifying circuit), and further, it is preferable that a function for amplifying at least one of a rectified voltage for charging a capacitor and a voltage applied to the bus line exists in the rectifying circuit.
The invention provides, as another means for solving the above problem, a method for controlling operation of an air bag system using the above igniter for an air bag system, wherein a time period for supplying a current from the capacitor to the heat generating portion is the time period from the point where a current value reaches the current value corresponding to 5% of the maximum current value to the point where it is reduced down to the value corresponding to 5% of the maximum current value, which is within 500 xcexcsec. In this case, the maximum current value in the period for supplying a current is a current value sufficient to ignite the priming.
In the case of a conventional air bag system, since a current for activating an igniter flows from a power source (a battery) with a relatively large capacitance at 1.2 A for about 2 msec, that is, at a relatively low current for a relatively long time, a waveform of an ignition current (a vertical axis denotes a current value (A) and a horizontal axis denotes a time (xcexc sec)) becomes rectangular.
In the present invention, however, since a current for activating an igniter is supplied from a capacitor with a relatively small capacitance, it is preferable that a relatively high electric current flows for a short time, because ignition of the igniter is made smoother and ignition energy itself can be made smaller. The waveform of the ignition current at this time (a vertical axis denotes a current value (A) and a horizontal axis denotes a time (xcexcsec)) becomes a discharging waveform expressed by the following formula (I) when discharging starts at a time of time t=0:
i(t)=(V0/R)xc3x97exe2x88x92t/CRxe2x80x83xe2x80x83(I)
(In the formula, v0 represents a capacitor charging voltage (V), R represents a circuit resistance (xcexa9), C represents a capacitor capacitance (xcexcF), t represents a time (xcexcsec), and i represents a current (A)).
When such a discharging waveform expressed by the formula (I) is employed, a current value becomes larger than a conventional rectangular waveform, but a current conduction time is shortened. Therefore, the ignition energy itself is reduced largely.
In the present invention, when a period in which a stable current supplying is being maintained after reaching a desired current value is defined as t (xcexcsec) and a period from a start of waveform rising to stopping of current supplying for making the heat generating portion generate a heat is defined as T (xcexcsec), it is preferable that a relationship (t/T) between these t and T is in the range of 0xe2x89xa6t/T less than 0.2 or 0.5 less than t/T less than 1.
In the case of 0xe2x89xa6t/T less than 0.2, a waveform of a current is similar to a discharging waveform (a waveform similar to a triangle) obtained when electricity stored in the capacitor is applied to the heat generating portion directly. In case of 0.5 less than t/T less than 1, a waveform of a current is similar to a waveform obtained when a discharging waveform is converted through a discharging waveform converting circuit (hereinafter, abbreviated as xe2x80x9ca waveform converting circuitxe2x80x9d) for converting a waveform of a current stored in a capacitor to a signal waveform of a current for igniting the priming or the like.
The period for supplying a current is as described above, and it is preferably within 200 xcexcsec, and more preferably within 100 xcexcsec. Incidentally, a current value at this time varies depending on a resistance value of the heat generating portion in the igniter, and it is determined on the basis of presence or absence of the waveform converting circuit, the constitution of the waveform converting circuit, a particle diameter of a priming, a shape of the heat generating portion and the like.
The invention provides, as another means for solving the above problem, a method for controlling operation of an air bag system using the above integrated circuit for an air bag system, wherein a current to the heat generating portion is supplied as an ignition pulse, and the current is supplied such that the width of the ignition pulse becomes 20 to 500 xcexcsec.
In the case of a conventional air bag system, since a current for activating an igniter flows from a power source (a battery) with a capacitance at 1.2 A for about 2 msec, that is, at a relatively low current for a relatively long time, a waveform of an ignition current (a vertical axis denotes a current value (A) and a horizontal axis denotes a time (xcexcsec)) becomes rectangular.
Therefore, in the above invention, a current is supplied at a relatively high electric current for a relatively short time, namely, a current is supplied such that the width of the ignition pulse is 20 to 500 xcexcsec, preferably 30 to 200 xcexcsec, and more preferably 40 to 100 xcexcsec. As a result, since an amount of ignition energy required for activating individual igniters can be reduced, the amount of ignition energy required for all the igniters, namely for the entire air bag system can be reduced. For this reason, the capacitance of the capacitor for backup power source incorporated into the ECU can be made smaller, and accordingly, the ECU itself can be reduced in size.
In the above invention, it is preferable, in view of reduction of the amount of a current, that a current is supplied such that the width of the ignition pulse becomes 40 to 100 xcexcsec.
According to the air bag system employing the present invention, the weight of the entire air bag system can remarkably be reduced by using the bus system and an operation performance similar to the conventional one can be ensured.